[Yvelina]

You simply cannot defend them. Province defense is useless against anything of consequence, and unless you are expecting attacks from scouts and assassins, anything above 1 point is a waste. You have to establish treaties and alliances, and convince your neighbors that they are better off attacking someone else. Later in the game, you can build castles, use teleport mages to kill off aggressors, but early game, diplomacy is your only option.

If you are talking about SP, there is nothing you can do. You will be attacked. The less your income and the higher the PD (1, 11, 21), the less chance a particular province will be attacked, but ultimately, all AIs will fight you.